They are molten when heated and harden upon cooling. These characteristics, which lend the material its name, are reversible so that it can be reheated, reshaped, and frozen repeatedly. As a result, thermoplastics are mechanically recyclable. Some of the most common types of thermoplastics are polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyethylene terephthalate and polycarbonate. (Source: Plastics Europe).